Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $205.92   12.190%   $231.0216   $231.02   $231.00   $231.00  
  Purchase #2 $138.26   3.678%   $143.3452   $143.35   $143.35   $143.30  
  Purchase #3 $51.77   7.567%   $55.6874   $55.69   $55.70   $55.70  
  Purchase #4 $154.55   3.373%   $159.763   $159.76   $159.75   $159.80  
  Purchase #5 $205.70   7.222%   $220.5557   $220.56   $220.55   $220.60  
  Purchase #6 $50.71   7.751%   $54.6405   $54.64   $54.65   $54.60  
  Purchase #7 $201.80   4.507%   $210.8951   $210.90   $210.90   $210.90  
  7 purchase totals = $1,008.71       $1,075.9085   $1,075.92   $1,075.90   $1,075.90